Solenoid construction



Jan- 8, 1935.' B. N. FOSTER `SOLENOID CONSTRUCTION Filed Aug. 24, 1954 Jf EB Inverzr: Bez'ymzn 2W Jozer,

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Patented Jan. 8, 1935 UNITED STATES SOLENOID CONSTBUCTICN Benjamin Norton Foster, Keene, N. H., anignor of one-half to Kingsbury Machine Tool Corporation, Keene, N. Hampshire H., a corporation of New Application Anim 24, 1934. semi No. 141,341

9Claims.

The present invention is an improvement in the construction of solenoids which are especially adapted for employment with alternating current.

One of the features of the present invention is the provision of a simply and cheaply constructed article which avoids excessive losses by eddy currents,

Another feature of the invention is the provision of a solenoid having an internal expansion spring which is protected by the solenoid structure from eddy current effects therein.

A further feature of the invention is the provision of a solenoid having a closely fitting and externally smooth housing of heat conductive nature which permits readily the dissipation of heat developed within the solenoid.

Still another feature of the present invention is the provision of a solenoid having a minimum of constructive parts, each of which is simply and cheaply manufactured and assembled.

Still another feature of the present invention` is the provision of a solenoid in which the pull curve" may be modified without extensive change or adjustment of the structure involved.

Still another feature of the present invention is the provision of a solenoid in which the parts are made of materials and of shapes which assure a minimum of wear and a long life for the structure.

With these and other features as objects in view, an illustrative form of practicing the invention is shown on the accompanying drawing. in which:

Figure 1 is a. diametrical sectional view.

Figures 2 and 3 are transverse sectional views substantially on lines 2-2 and 3-3 of Figure 1.

Figure 4 is an end elevation.

Figures 5 and 6 are side elevations, of one end piece.

Figure 'I is a side elevation of another end piece.

Figure 8 is a sectional view substantially on line 8-8 of Figure 7.

Figure 9 is a view corresponding to Figure 1. but showing an assemblage of parts for attaining a different pull curve.

In the drawing, the structure is enclosed in an outer housing 10 of metal having a smooth external surface which is illustrated as cylindrical. A reduced portion 11 connects the portion of major diameter with a neck portion 12 of lesser diameter. The open end of the larger portion 10 is provided with internal screw threads to receive a closing and securing plug 13. This plug has a cavity on its inner face which (Cl. F15-438) closely engages the external surface of and aligns a winding sleeve 14 which itself has a shoulder 15 leading to angenlarged portion 16 -which is tightly received within the cavity of the portion 12 of the outer casing.

A thin coil head or end member 1'1 (Figures 1, 5 and 6) has three radial pins 18 which extend into apertures of the winding sleeve 14. A second head or end member 19 (Figures 1, 7 and 8) similarly has three pins 20 which extend into the winding sleeve 14. These pins therefore Serve in the preliminary assembly of the winding sleeve and the end members preparatory to the winding of a coil 21 therein. It will be noted that this preliminary assembly is mechanically rigid and that the winding of the coil may occur on a lathe or normal type of winding machine and that this coil may be impregnated and baked in the usual way if so desired.

A movable core or armature member has a slotted head end 25 with an aperture 26 by which it may be connected as usual to a link which is to be actuated thereby. This armature is slidable in and closely fits the internal surface of the winding sleeve 14 which as illustrated is cylindrical and concentric with the outer casing. A central axial hole 27 is provided in the armature for receiving an expansion spring 28. Further, the armature is slotted longitudinally at a number of places as shown in Figure 2 to provide kerfs 29 which serve to interrupt electrical circuit paths for eddy currents. One of these kerfs 29a extends to the hole 27 so that there is provided no complete circuit for eddy current, while the other kerfs 29 are illustrated as terminating short of this hole and operate to restrict localized eddy currents within the mass of the armature.

A pole piece or stop member 30 which similarly is provided with kerfs 29, 29a (Figure 3) has akcavity 31 for receiving the other end oi the expansion spring 28 and hasla`threaded aperture which is engaged by a screw 32 which extends through the closing plug 13 and serves to hold the pole piece 30 iixedly in position and in supporting relation to the sleeve 14.

It is preferred to cut away the abutting edges of the armature and pole piece (Figure 1) to provide recesses 33 which receive any oil or dirt which may be scraped from the internal wall of the winding sleeve 14, and thus permit the armature to come into abutting relation with the stop member or pole piece 30.

In assembly, when the parts have been pre pared and winding has been assembled upon the thereof. The winding sleeve .14 is now slid into position with its enlarged en`d 16 closely received by the reduced end 12 of the casing 10 until the end member 19 engages fixedly witha casing asa stop to limit the further inward movement of these parts. A pin 19p of member 19 enters the slot 10a of the casing 10 (Figure 4) and prevents relative rotation of the sleeve and its winding with. respect to the casing, so as to avoid shearing of the leads 36, 37. The spring 28 is inserted in the stop member 30. 'Ihe plug 13 is then screwed into position until it engages and supports the winding sleeve and holds the assembly of the winding sleeve and its winding tightly in position in the casing 10; this operation is performed by a suitable wrench engaged in holes 13b. 'Ihe screw 32 is then inserted and/or tightened and the plug operates thereafter to complete the interrupted magnetic shield and to hold the associated parts rigidly and tightly in position.

In order to assure a minimum of wear of the parts, the amature 25 and preferably also the stop member 30 and winding sleeve 14 are coated at least at their engaging faces with chromium. This material has been found advantageous, as a very thin layer of it provides excellent security against excessive wear and yet does not modify the magnetic properties of the parts, as might be the case if case-hardening or like treatment other than treatment for optimum magneticA effects were given to these members.

In order to reduce losses by eddy currents, the winding sleeve 14 and also the outer casing 10 and plug 13 preferably have corresponding slots 14a, 10a, 13a as shown, as this prevents a direct and simple circuit for ow of eddy currents in a direction parallel or concentric with the turns of the winding itself.

The proportion of the total length which is utilized for the pole piece and for the armature will vary according to the demand for a particular type of pull curve. Thus, as the pull falls oil very rapidly as the armature or plunger moves away from the pole piece, and naturally this pull is very high at the position of abutment of the parts, it is possible by changing the relative lengths of pole pieces and armatures, as illustrated in Figures 1 and 9, to produce a marked hump in the pull curve at substantially any point desired.

With the form shown in Figure 1, the hump oc'- l curs substantially at half-stroke., The sub-division of the solid amature, by' providing the radial kerfs, changes the total amount of iron in the magnetic circuit and the character of the hump may be modified by changing the size and number -of such kerfs.

yon alternating current as no circuits are provided for the movement of eddy currents, all of the parts being slotted to avoid such ow. In par-- ticular, it is found that the structure of the armature and pole piece of solid material, with 'slots formed therein, is not only advantageous mechantically as providing an easy manner of assemblage (in preference to laminations) but also it permits the use of an internal expansion spring 23 for separating the parts upon deenergization of the winding. This spring, however, is protected by the magnetic shield formed by the surrounding armature and pole piece when the parts are in abutment, which is the normal condition during energization of the coil. Therefore, no such flow of eddy currents occurs in the spring such esto weaken or modify its elastic property.

Owing to the smooth external shape of the casing 10 and its closing plug 30, the solenoid may be7 located and maintained in a cavity of substantially the same size in the frame of a mechanism which-is to be controlled thereby. Thus, it may be inserted in a housing H (Figure 1) in close contact therewith so that the heat generated by electrical losses in the coil are transmitted to the casing 10 and thus to the housing H. Like` wise, any heat produced by eddy currents in the casing 10 -is likewise transmitted. It. will be noted that the walls of kerfs 29 in the armature and pole piece similarly operate as radiation surfaces and the movement of the armature causes a pump-like action to ventilate and cool these parts. Hence it is found in practice that the solenoid has 'a great eiiiciency as it operates at high current and magnetic intensities without excessive heat losses and with a rapid transfer of such heat as is generated.

It is obvious that the invention is not limited solely to the form of construction shown, but that it may be modified in many ways within the scope of the appended claims.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent, is:

- l. A solenoid structure especially for alternating currents comprisingl a hollow metal casing having a longitudinal slot, a metal winding sleeve having a longitudinal slot, a winding on said sleeve, a closing plug for said casing and having a radial slot, and an armature movable in said sleeve, said slots operating to interrupt the paths of eddy currents.

2. A solenoid structure comprising a hollow casing having an end aperture, a winding sleeve supported in said aperture, and a closing plug for said casing having a shoulder for supporting said sleeve at a point remote from said aperture."

3. A solenoid structure especially for alternating currents, comprising ahollow casing having a reduced end, a winding sleeve supported insaid reduced end, end members secured on said sleeve, a winding on said sleeve having its terminals extending through the reduced end, and a closing plug for said casing engaging said sleeve, one of said end members cooperating with said reduced end in positioning said sleeve in said casing.

4. A solenoid structure especially for alternating currents, comprising a hollow casing, a winding sleeve in said casing and a winding thereon, an armature slidable in said sleeve and comprising a block of magnetizable metal having a plurality of longitudinal kerfs therein, one of said kerfs completing an air gap from the axis o! the armature to its periphery to prevent the circuit of eddy currents therearound.

5. A solenoid structure especially for alternating currents, comprising a sleeve having a winding thereon, an armature member having a plurality of longitudinal kerfs and an axial cavity extending from its inner end, a stop member having an axial cavity alined with said tlrst cavity, and an extension spring located in said cavites and protected by said armature and stop members when said members are in abutting relation.

6. A solenoid structure comprising a sleeve having a winding thereon, an amature member and a stop member each having an axial cavity, an extension spring located in said cavities and protected by said members when they are in abutting relation, the lengths of the said members being constructed and arranged to provide a hump on the the pull curve" at a predetermined point, said members having longitudinal external keris thereon for interrupting eddy currents and for distributing the magnetizable metal to give said hump a predetermined characteristic.

1. A solenoid structure comprising a sleeve having a winding thereon, and an annature member having a case of magnetizable material of selected magnetic properties, said case being coated with chromium to protect the same against wear and deterioration without inuencing the magnetic properties thereof.

8. A solenoid structure comprising a sleeve having a winding thereon, a stop member and an armature member closely fitting in and guided by said sleeve, said members having longitudinal external kerfs therein, the edges of the members being cut away between the kerfs for permitting the members to come into abutting relation regardless of material scraped from the sleeve at said edges.

9. A solenoid structure especially for alternating currents, comprising a sleeve having a winding thereon, an armature member having an axial cavity extending from its inner end, a stop member cooperative with said armature member, and an extension spring having an end in said cavity and guided by said armature member, said spring being protected by said armature and stop members when said members are in abutting relation, said armature member having a longitudinal air gap extending from its cavity to its outer surface to interrupt the path oi eddy currents.

BENJAMIN NORTON FOSTER. 

